In prior art light emitting devices it is known to use LEDs to facilitate putting light guides close to the light emitting area of the light source of the light emitting device to obtain a high coupling efficiency. For LEDs with primary lenses a side reflector is necessary for obtaining high coupling efficiencies.
With flat emitting sources such as Medium Power LEDs and flat (remote) Phosphor modules it is possible to put light guides very close to the emitting surface with high coupling efficiencies.
Going from a flat PCB with lambertian light sources to a more all around light emission and at the same time moving the emitting surface upwards for a better filament like look and feel it is necessary to bend the light guide. A prior art light emitting device with a light guide unit comprising a light guide with a bent section is described in US 2012/0026748.
However, the maximum possible bending of the light guide without light leakage occurring is restricted. For illustrative purposes, FIG. 1 shows a bent light guide L. Light can be guided from a top to a side emitting plane. The maximum bending, that is the minimum radius R, of the light guide L with no light leakage occurring from the sides is dependent on the thickness d of the light guide. The maximum of the ratio R/d with no light leakage occurring is also dependent on the refractive index of the light guide and its surroundings, which may e.g. be air or alternatively a suitable and preferably transparent cladding.
For light sources which have a relatively large emitting area compared to the total available space in the light emitting device the limitations on the maximum bending is a problem, which may lead to unwanted light leakage occurring through the side surfaces of the light guides of the light emitting device. This in turn results in a compromised light distribution of the light emitting device.